U.S. patent number 4,044,374 [Application Number 05/650,396] was granted by the patent office on 1977-08-23 for semiconductor device header suitable for vacuum tube applications.
This patent grant is currently assigned to Texas Instruments Incorporated. Invention is credited to Wayne W. Chan, Dean R. Collins, Charles Grady Roberts.
United States Patent |
4,044,374 |
Roberts , et al. |
August 23, 1977 |
Semiconductor device header suitable for vacuum tube
applications
Abstract
A disk shaped ceramic support has a mounting surface provided as
a unitary part of the support with conductors extending generally
outward from the mounting surface through the thickness dimension
of the support, the outer ends of the conductive leads being
connected to a ring of terminal leads. A charge coupled device
(CCD) imager chip is secured to the mounting surface to leave a
backside illumination surface of the chip unobstructed and
electrical interconnections are made from terminal pads on the
front surface of the chip to the ends of the conductive leads
adjacent the mounting surface. A cover plate attached to the
insulating support outwardly of the interconnections encloses the
front surface of the chip. In a preferred structure the chip is
mounted on an apertured molybdenum disk unitarily attached to the
support with the illumination surface of the CCD chip facing the
aperture. A peripheral tube flange can be brazed to the periphery
of the insulating support and a tubular enclosure vacuum sealed to
the tube flange for accommodating a photo-cathode source which
faces the illumination surface of the imager chip. In a further
embodiment, the front side of the chip is attached directly to a
mounting surface provided by the insulating support itself,
connections between the terminal pads on the chips and the
conductive leads of the support being effected therough apertures
in the support located adjacent corners of the chip.
Inventors: |
Roberts; Charles Grady (Plano,
TX), Chan; Wayne W. (Plano, TX), Collins; Dean R.
(Dallas, TX) |
Assignee: |
Texas Instruments Incorporated
(Dallas, TX)
|
Family
ID: |
24608731 |
Appl.
No.: |
05/650,396 |
Filed: |
January 19, 1976 |
Current U.S.
Class: |
257/225;
257/E23.067; 257/695; 257/703; 257/680; 257/697 |
Current CPC
Class: |
H01J
9/24 (20130101); H01J 29/02 (20130101); H01J
29/92 (20130101); H01J 31/26 (20130101); H01L
23/49827 (20130101); H01L 2224/48091 (20130101); H01L
2224/4824 (20130101); H01L 2224/49171 (20130101); H01L
2924/01014 (20130101); H01L 2924/01039 (20130101); H01L
2924/01079 (20130101); H01L 2924/15312 (20130101); H01L
2924/1532 (20130101); H01L 2924/16195 (20130101); H01L
2224/48091 (20130101); H01L 2924/00014 (20130101); H01L
24/48 (20130101); H01L 24/49 (20130101); H01L
2224/4824 (20130101); H01L 2224/49171 (20130101); H01L
2924/00 (20130101); H01L 2924/10253 (20130101); H01L
2924/10253 (20130101); H01L 2924/00 (20130101); H01L
2924/00014 (20130101); H01L 2224/05599 (20130101); H01L
2924/00014 (20130101); H01L 2924/00014 (20130101); H01L
2224/45099 (20130101) |
Current International
Class: |
H01J
29/02 (20060101); H01L 23/48 (20060101); H01J
31/26 (20060101); H01J 31/08 (20060101); H01L
23/498 (20060101); H01J 29/00 (20060101); H01J
29/92 (20060101); H01J 9/24 (20060101); H01L
039/02 (); H01L 029/78 (); G01T 001/24 (); H01L
023/02 () |
Field of
Search: |
;357/24,80,29,74 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Proc. Sym. on CCD Tech. for Scientific Imaging Applications, Cal.
Tech., June 1975; Collins et al. .
Inter. Conf.-Tech. and Applications of CCD's-Univ. of Edinburgh,
Sept. 25-27, 1974; Gray et al. .
Inter Conf. on Applications of CCD's-Oct. 29-31, 1975; Barton et
al..
|
Primary Examiner: Wojciechowicz; Edward J.
Attorney, Agent or Firm: Levine; Harold Grossman; Rene' E.
Comfort; James T.
Claims
What is claimed is:
1. A header assembly including a charge transfer device chip having
a plurality of spaced apart terminal pads on one surface thereof,
an insulating support; a mounting surface unitary with said
support; a plurality of conductive leads affixed to said support
member and extending generally outwardly from said mounting
surface; means fixedly mounting said charge transfer device chip on
said mounting surface; respective electrical interconnections
between said terminal pads and said conductor leads; and cover
means surrounding said chip in vacuum-tight sealed relation with
said insulating support to enclose said electrical interconnection;
said conductive leads extending beyond said cover means; means
hermetically sealing said conductive leads along the lengths
thereof between the interior and exterior of said cover means; and
terminal leads electrically connected with said conductive leads
externally of said cover means.
2. A header assembly according to claim 1 wherein said charge
transfer device has an illumination surface on one surface of said
chip opposite from the surface at which said terminal pads are
located; and said mounting surface comprises a surface surrounding
an aperture in said insulating support, said aperture being aligned
with and exposing said illumination surface.
3. A header assembly according to claim 2, wherein said
illumination surface is provided by a locally thinned area of said
charge transfer device chip; and wherein said chip includes a
peripherally thickened area surrounding said illumination surface
positioned on and affixed to said mounting surface.
4. A header assembly according to claim 2 in combination with
enclosure means vacuum-tight sealed to said header assembly and
enclosing said illumination surface with a vacuum therein; and
wherein said insulating support includes at least one aperture for
equalizing pressure on opposite sides of said charge transfer
device chip.
5. A structure according to claim 4, including photo-cathode means
disposed within said enclosure means and facing said illumination
surface.
6. A header assembly according to claim 1, wherein said conductive
leads extend outwardly from said mounting area within the thickness
dimension of said insulating support, said leads being exposed
adjacent said mounting surface for making said electrical
interconnections thereto.
7. A header assembly according to claim 1, including at least one
aperture extending through said insulating support and aligned with
said terminal pads on said charge transfer device chip, and wherein
said electrical connections between said terminal pads and said
conductor leads extend through said aperture.
8. A header assembly according to claim 1, wherein said charge
transfer device chip is rectangular and said terminal pads are
located adjacent a plurality of corners thereof; said mounting
surface is provided by said insulating support; a plurality of
spaced apertures extending through said insulating support and
aligned with said terminal pads; wherein said electrical
connections between said pads and said conductor leads extend
through said apertures; and means sealedly affixing said charge
transfer device chip to said mounting surface for providing between
said chip and said mounting area a seal surrounding said
apertures.
9. A header assembly according to claim 1, wherein said mounting
surface comprises a member unitarily attached to said insulating
support and comprising material providing a thermal match with the
semiconductor material of said chip.
10. A header assembly according to claim 9, wherein said charge
transfer device chip comprises a silicon chip and said mounting
surface comprises molybdenum.
11. A header assembly according to claim 1, wherein said terminal
leads extend in a coplanar array externally of said cover
means.
12. A header assembly according to claim 1, including support
material for said charge transfer device chip filling the space
between said chip and said cover means.
13. A header assembly including a charge transfer device chip
having a plurality of spaced apart terminal pads on one surface
thereof and an opposite surface providing an illumination surface;
a ceramic insulating support having a mounting surface unitary
therewith and comprising a seating surface surrounding an aperture
through the insulating support; said charge transfer device chip
being fixedly secured to said seating surface with said
illumination surface aligned with and facing said aperture and with
said terminal pads remote from said aperture; a plurality of
conductive leads extending generally outwardly from said mounting
area within the thickness dimension of said insulating support,
said conductive leads having exposed surfaces adjacent said
mounting area; respective electrical interconnections between said
terminal pads and said exposed portions of said conductive leads;
cover means surrounding said charge transfer device chip in
vacuum-tight sealed relation with said insulating support and
enclosing said electrical interconnections; and a plurality of
terminal leads electrically connected with said conductive leads
exteriorly of said cover means.
14. A header assembly according to claim 13, wherein said seating
surface comprises an apertured member fixedly secured to said
insulating support, said apertured member comprising a material
providing a thermal match with the semiconductor material of said
charge transfer device chip.
15. A header assembly according to claim 14, wherein said apertured
member comprises an apertured molybdenum disk and said charge
transfer device chip comprises a silicon chip.
16. A header assembly according to claim 14, wherein said apertured
member provides an equipotential surface surrounding said charge
transfer device chip.
17. A header assembly according to claim 13, further including
enclosure means sealed with said header assembly to maintain a
vacuum within said enclosure; and photo-cathode means disposed in
said enclosure means and facing the illumination surface of said
charge transfer device chip.
18. A header assembly including a charge transfer device chip
having a plurality of spaced apart terminal bonding pads on one
surface thereof; an insulating support; a plurality of conductive
leads imbedded within the thickness of said support; said
conductive leads having outer ends exposed at a first surface of
said support and inner ends connected with a spaced array of
projecting bonding surfaces at the opposite surface of said
support; said bonding pads of said charge transfer device chip
being aligned with and directly bonded to said projecting bonding
surfaces to mount said charge transfer device on said support with
said bonding pads electrically and physically connected with said
projecting bonding surfaces; and terminal leads electrically
connected with said terminal surfaces on said first surface of said
support; said charge transfer device chip further having an
illumination surface on a surface thereof opposite said bonding
pads.
19. A header assembly according to claim 1 wherein said cover means
includes a ring-shaped metal member sealed in vacuum-tight relation
with said insulating support and a metal cover member welded to
said ring member in vacuum-tight relation therewith.
20. A header assembly according to claim 19, wherein said cover
member is a dish-shaped member accommodated within said ring-shaped
member.
21. A header assembly according to claim 20, wherein said metal
cover member is welded to said ring-shaped member using a
non-oxidizing atmosphere welding process.
22. A header assembly including a charge transfer device chip
having a plurality of spaced apart terminal pads on one surface
thereof and an opposite surface providing an illumination surface;
a ceramic insulating support having a mounting surface unitary
therewith and comprising a seating surface surrounding an aperture
through the insulating support; said charge transfer device chip
being fixedly secured to said seating surface with said
illumination surface aligned with and facing said aperture and with
said terminal pads remote from said aperture; a plurality of
conductive leads extending generally outwardly from said mounting
area within the thickness dimension of said insulating support,
said conductive leads having exposed surfaces adjacent said
mounting area; respective electrical interconnections between said
terminal pads and said exposed portions of said conductive leads;
and a plurality of terminal leads electrically connected with said
conductive leads exteriorly of said cover means.
Description
This invention relates to header devices for semi-conductor
photo-electric elements, more particularly for charge transfer
imager devices, and to structures incorporating such header
assemblies.
It is desirable to provide such a header assembly wherein the
illumination surface of the device is not subject to obstruction,
wherein the semiconductor element may be mounted with minimal
possiblities of damage thereto during assembly, and wherein
electrical connections between terminal pads of the semiconductor
element, conductors forming part of the header assembly and
external terminal leads to the conductors may relatively easily be
effected. When the header assembly itself is to form part of the
closing wall of an eventual structure incorporating the header
assembly, a vacuum seal along the length of the conductive paths
between the external terminal pins and the interior of the
structure also is required.
The present invention provides a header assembly including a charge
transfer device chip having a plurality of spaced apart terminal
pads at one surface thereof. The charge transfer device chip is
fixedly mounted on a mounting surface provided as a unitary part of
an insulating support, leaving the illumination surface of the chip
unobstructed. Electrical interconnections are made between the
terminal pads and conductive leads fixed to the support member and
extending generally outwardly from the mounting area. Cover means
surrounds the chip in hermetically sealed relation with the
insulating support to enclose the electrical interconnections. The
conductive leads extend beyond the cover means and are vacuum
sealed along the lengths thereof between the interior and exterior
of the cover means. Terminal leads are secured and electrically
connected to the conductive leads externally of the cover
means.
In a preferred header assembly, the charge transfer device has an
illumination surface on a surface of the chip opposite from the
surface at which the terminal pads are located, and the
illumination surface may be provided at a locally thinned region of
the charge transfer device chip.
The mounting area of the support may then comprise a seating
surface surrounding an aperture in the insulating support, the
aperture being aligned with the illumination surface.
Advantageously the seating surface comprises a material which is
thermally compatible with the semiconductor material of the charge
transfer device chip, for example when using a silicon chip a
molybdenum seating surface may be utilized.
Header assemblies embodying the invention may be utilized in
constructing, for example, photo-inverter imaging tube structures,
proximity tube structures, and imager devices.
For a more detailed description of illustrative features of the
invention, several embodiments thereof will be described in further
detail with reference to the drawings wherein:
FIG. 1 is a section of a header assembly embodying the invention
along the line II--II of FIG. 2;
FIG. 2 is a top plan view of FIG. 1;
FIG. 3 is a sectioned, isometric view of the assembly shown in
FIGS. 1 and 2;
FIG. 3a is a pictorial section of a proximity tube including the
header assembly of FIGS. 1 - 3;
FIGS. 4a and 4b are, respectively, pictorial plan and sectional
views of another embodiment of the invention;
FIGS. 4c, 4d and 4e are pictorial sections of structures
incorporating the header assembly shown in FIGS. 4a and 4b;
FIG. 5 is a section of part of a further embodiment of the
invention;
FIG. 6 is a section of part of a header assembly that is a
modification of that shown in FIG. 5;
FIGS. 7 and 8 are pictorial sections through different parts of a
further header assembly embodying the invention;
FIGS. 9 and 10 are, respectively, top and bottom plan views of part
of FIGS. 7 and 8; and
FIG. 11 shows an enlarged detail of FIG. 10.
FIG. 12 is a cross-sectional view of another embodiment of a header
assembly embodying the invention.
The header assembly shown in FIGS. 1 to 3 includes a disk-shaped
insulating support 10, suitably ceramic, having a central
rectangular aperture 12 on the underside of which, as seen in FIGS.
1 and 3, is brazed a metal disk 14 having a central rectangular
aperture 16. Adjacent the aperture 12, the insulating support 10
has a thinned annular portion 18 to the depressed upper surface of
which (FIGS. 1 and 3) electrically conductive leads 20 are bonded,
the leads extending generally outwardly from the aperture 12 buried
within the thickness dimension of the support 10 (being
hermetically sealed thereto along the lengths of the conductors 20)
beyond a seal flange 22. The seal flange 22 is suitably made of
KOVAR and is brazed to a metal ring screen printed on the upper
surface of the insulating support 10 adjacent the periphery of the
aperture 12. The conductors 20 have feed through portions 21 at the
outer ends thereof to which are secured terminal pins 24
surrounding the sealing flange 22 and extending concentrically
therewith.
A semiconductor imager device, shown as a charge coupled device
(CCD) image chip 26 (the construction of which may be conventional
and need not be described in detail herein) is mounted on the metal
disk 14. The chip 26 has a locally thinned central area defining an
illumination surface 28 on the lower side thereof (FIG. 1) which is
positioned in facing alignment with the aperture 16 in the disk 14,
a thickened area 30 of the chip 26 which surrounds the illumination
surface being alloyed to the metal disk 14. The upper surface of
the chip 26 includes various electrodes including phase-electrodes
on an insulating layer on the surface of the semiconductor chip and
overlying the thinned illumination surface 28 of the chip.
Electrical conductors to the electrodes and other conventional
structures, e.g. signal input and output structures, of the CCD
device are formed on the insulating layer on the upper surface of
the chip in conventional manner and extend over that surface to
conductive terminal pads 36 adjacent the edges of the chip. Wire
connections 38 are bonded between the terminal pads 36 and the
exposed portions of the conductive leads 20 adjacent the aperture
12. One of the conductive leads 20 is electrically connected with
the disk 14.
The structure so far described provides a compact and rugged header
assembly for the CCD imager chip.
In a particular application of the header assembly in conjunction
with a photo-cathode source to provide a proximity tube structure,
as depicted in FIG. 3a, the insulating support 10 is attached to a
peripheral cup-shaped flange 37 in vacuum-tight sealed relation
therewith and, in turn, an enclosing tubular member 40 is
vacuum-tight sealed to the flange. The sealing flange 22 is closed
by a cover member 23 vacuum-tight sealed thereto and a vacuum drawn
within the enclosure. The insulating support 10 includes apertures
42 for equalizing the pressure on both sides of the CCD chip
26.
A photo-cathode 44 is mounted in a radiation-transmissive end wall
of the tubular enclosure 40, the emission surface 46 of the
photo-cathode facing the illumination surface 28 of the CCD chip.
The photo-cathode 40 may be of conventional structure, for example
as described in Kazan, B. and Knoll, M., Electronic Image Storage,
Chapter 1, Sect. C, pp. 51-67, Academic Press, N.Y., 1968.
In fabrication of the structure shown in FIGS. 1 to 3, the
conductive leads 20 are first screen printed in conventional manner
on the surface of an unfired (green) ceramic disk, suitably 94%
alumina, in which the aperture 12 has been punched, and then
covered by a second annular ceramic disk, again suitably 94%
alumina, positioned to define the depressed surface 18 on which the
leads 20 are exposed adjacent the aperture 12. The feed through
members 21 are also formed at this stage. The resultant assemblage
is then fired to produce a unitary assembly comprising the
insulating support, conductive leads 20 extending to the
feed-through members 21 and vacuum-tight sealed within the
thickness dimension of the insulating support 10 as shown in FIGS.
1 to 3. The metal disk 14, sealing flange 22, and flange 38 are
then brazed onto metal surfaces previously screen printed on the
support member 10. The molybdenum disk 14 is preferably extended in
diameter to occupy the whole impingement area of electrons from the
photo-cathode, to provide an equipotential surface on the support
10, and so preventing localized charge build up of the support
surface. Then the terminal pins 24 are brazed to the terminal
members 21. The exposed surfaces of the conductors 20, metal disk
14 and terminal pins 24 are gold plated prior to the surface
oxidation thereof.
The CCD chip is then positioned on the metal disk 14 with the
illumination surface 28 facing and exposed by the aperture 16 and
gold alloyed to the disk 14. The metal disk 14 provides a thermally
compatible support surface for the chip 26 and when, as is typical,
the chip is a silicon chip the disk 14 suitably is a molybdenum or
tungsten disk. The wire bonds 38 are then effected between the
terminal pads 36 and the ends of the conductive leads 20 adjacent
the aperture 12.
A dish-shaped KOVAR cover plate 23 is then welded to the rim of the
seal flange 22 suitably made of KOVAR, to effect a vacuum-tight
seal therewith. After mounting the tubular enclosure 40, with the
photo-cathode 44 disposed in the end wall thereof in facing
relation with the illumination surface 28 of the CCD chip 26, the
tubular member 40 is welded to the cup-shaped flange 37 again to
effect a vacuum-tight seal therewith. The welds -- shown at W --
are preferably effected using an inert-gas or non-oxidizing
atmosphere welding process, e.g. a helium-arc welding process.
The resulting structure is then subjected to a bake-out cycle,
suitably within the temperature range 300.degree. to 500.degree. C,
dependent on the metal or metal-combination used for the conductor
leads, to release any occluded gasses in the component parts of the
structure and then a vacuum, typically .ltoreq.10.sup.-9 mmHg is
pulled inside the structure. It will be appreciated that the
component parts within the structure, including the insulating
supports 10, the various conductors and the several seals and
brazed joints must be capable of withstanding the temperature of
the bake-out cycle and of maintaining the integrity of the vacuum
during operation of the structure. Such materials are known in the
tube sealing and semiconductor art and need not further be
identified.
Furthermore the location of the conductors 20 buried within the
thickness dimension of the support 10 is an advantageous manner of
maintaining the hermetic integrity of the seal between the leads
and the support material.
The header assembly described with relation to FIGS. 1 to 3 is
useful in the construction of a proximity tube, as shown in those
figures, but also may be employed, for example, in constructing an
inverter tube wherein the photo-cathode would be mounted facing and
separated from the illumination surface 28 of the CCD chip 26 by an
electrostatic or magnetic lens system.
Furthermore, it is to be appreciated that the header assembly
described with reference to FIGS. 1 to 3 may be useful in providing
an imaging structure wherein a window, for example a quartz window,
covers the illumination surface 28 of the CCD imager and is sealed
to the surface of the support 10. Such a structure would be useful,
for example, in a space environment, since condensation on the
window and the imager surface 28 would be obviated. In such a
structure, the flange 37 would not be essential.
A further embodiment of the invention is illustrated by FIGS. 4a to
4e, component parts which are the same as those shown in FIGS. 1 to
3 being identified by like references.
The header assembly shown in FIGS. 4a and 4b includes an insulating
disk-shaped ceramic support 50 having a central aperture 52, a
backside illuminated CCD imager chip 26 having its peripheral
portion 30 alloyed to a metalized area of the support 50 so that
the illumination surface 28 faces and is aligned with the aperture
52. The terminal pads 36 on the surface of the chip opposite from
the illumination surface 28 are electrically connected by bonded
wires 38 to conductive leads 20 screen printed on the surface of
the support 50 and extending generally radially from the aperture
52.
FIGS. 4c - 4e show completed structures incorporating the header
assembly of FIGS. 4a and 4b. The structure shown in FIG. 4c
includes a tubular ceramic wall 54 one end of which is closed by a
ceramic plate 56 including a photo-cathode structure 58, and the
other end by a ceramic coverplate 60, to provide a vacuum-tight
enclosure within which the header assembly 62 is attached by wires
64 between the conductors 20 and external terminal leads 66
extending in a coplanar array radially through the tubular member
54 and hermetically sealed therewith. The wires 64 have sufficient
rigidity to securely maintain the assembly 62 in proper position
during operation of the structure.
The structure shown in FIG. 4d is similar to that shown in FIG. 4c
except that the insulating support 50 itself forms part of the wall
of the enclosure, the first ceramic tubular member 68 being sealed
to the underside of the support 50 and a separate ceramic tubular
member 70 being sealed to the upper surface thereof, the conductive
leads 20 extending externally of the tubular member 70 in
hermetically sealed relation therewith. A coplanar ray of external
conductor leads 72 is bonded to the conductors 20.
FIG. 4e shows an alternative to the structure of FIG. 4d, wherein a
ring of terminal pins 74 are secured to the conductors 20 and
extend concentrically with the tubular member 70.
FIG. 5 shows a modification of the header assembly shown in FIGS. 1
to 3 wherein the conductive leads 20 terminate short of the
aperture 12, leaving a seating surface 77 of the annular portion
18, the CCD chip 26 being alloyed to a metalized portion of the
surface 77. The space between the CCD chip 26 and the cover plate
23 may be filled with a material 76 to provide additional backing
support for the CCD chip 26. For example, the material 76 may
suitably comprise an epoxy resin. When fabrication of a structure
incorporating the header assembly involves a bake cycle and
operation of the structure requires maintenance of a vacuum-tight
enclosure, the apertures 42 and regions between the chip and the
apertures 42 would previously be hermetically sealed for example
using a tin, lead or glass sealing material so that detrimental
outgassing from the epoxy resin would be prevented.
Alternatively, the space between the CCD chip and the cover plate
23 may be left unfilled, the apertures 42 then providing pressure
equilization on both sides of the CCD chip as described with
reference to FIGS. 1 to 3.
Use of materials other than epoxy resin for the filler material 76
may pose problems in avoiding thermal stressing of the CCD chip 26
during high temperature firing cycle carried out after the chip has
been mounted.
FIG. 6 shows an alternative structure to that of FIG. 5 in which
the support 10 does not include a central aperture 12 but instead
provides a mounting surface 78 to which the surface of the CCD
surface opposite the illumination surface 28 is secured. The CCD
chip is secured using a high grade epoxy resin, for example, such
as that commercially available under the designation ABLESTICK
642-1. The terminal pads 36 are located adjacent corners of the CCD
chip and aligned with separate apertures 80 through the insulating
support 10 and through which the bonding wires 38 extend.
As will be noted in FIG. 6, the lower surface of the support 10 is
recessed to accommodate the chip 26, the edges of which are secured
to the walls of the recess 82 using a sealing material, again for
example tin, lead, indium or glass, to ensure a hermetic seal so
that the epoxy resin is not exposed to outgassing or vacuum
conditions during fabrication and operation of a structure
including the header assembly.
Another embodiment of a header assembly embodying the invention is
shown in FIGS. 7 to 11.
The insulating support 84 is constructed using three ceramic layers
86, 88 and 90. While in a green or unfired state, an aperture 92 is
punched in the layer 86 to accommodate the CCD chip 26 while
apertures 94 are punched in the layer 88 to align with areas
adjacent the corners of the CCD chip at which the terminal pads 38
are located, as shown in greater detail in FIG. 11. On the under
side of the layer 88, conductor leads 20 are screen printed, the
leads 20 extending to locations adjacent each of the apertures 94.
The layer 90 includes apertures 96 that are oversize relative to
the apertures 94 and registered therewith to expose end portions of
the conductive leads 20. The structure thus far described is fired
to produce a unitary assembly comprising the support 84.
The CCD chip 26 is located and sealed in the recess 92 using an
adhesive 98 such as, for example, glass or epoxy resin to seal the
front (lower as seen in FIGS. 7 and 8) and peripheral surfaces of
the CCD chip in the recess 92.
FIG. 7 is a part section of the header assembly in a region thereof
at which no terminal pads 38 are located while FIG. 8 shows a
similar part section through a region in which there are terminal
pads 38, i.e. adjacent corners of the CCD chips 26. Both figures
show the illumination surface 28 of the CCD chip facing the mouth
of the recess 92 as also illustrated in the plan view of FIG.
9.
The terminal pads 36 are connected to the conductive leads 20 by
bonded wires 38 extending through the apertures 94, the apertures
96 providing access to effect the bonding operations. The
particular locations of the terminal pads 36, conductive leads 20,
bond wire 38 and apertures 94 and 96 are shown in more detail in
FIGS. 10 and 11. FIG. 10 shows a lower plan view of part of FIG. 7
in the region of the CCD chip 26 while FIG. 11 shows a detailed
plan view in the region of one of the apertures 96. If so desired
the apertures 94 and 96 may be filled with epoxy resin.
In relation to each of the above structures, in choosing a suitable
adhesive or sealing material, factors which may need to be
considered include the amount of thermal cycling expected during
the fabrication of the header assembly and during operation of a
structure incorporating the header assembly; potentially
deleterious effects of the adhesive or sealing material on the CCD
chip; the vacuum integrity of the seals effected; ease of
application, and, in the case of adhesive used as a backing
material for the CCD chip, the uniformity of support behind the
thinned area of the chip.
In relation to the structures described with reference to FIGS. 4e
to 7, it will be appreciated that connection of external terminal
pins to the outer ends of the conductors 20 may be effected as
described with reference to the pins 24 in FIGS. 1 to 3, or
radially extending terminal conductors may be provided as described
with reference to FIG. 4c.
A further embodiment is depicted in FIG. 12 in which the ceramic
support 100 includes conductive leads buried therein and
terminating, at their inner ends, in bonding bump pads 104 which
are aligned with and bonded to bonding bump pads 102 on the front
(upper) surface of the CCD chip 26. The bonding process may be
carried out using so-called flip chip bonding techniques known in
the semiconductor art. It will be appreciated that FIG. 12 is
diagrammatic only and that in practice, after the bonding
operation, the front surface of the chip would be substantially
flush with the underside of the support 100. This embodiment
provides a relatively simple structure since the support requires
no aperture for mounting the chip 26 and the bonded
interconnections 38 are dispensed with thereby simplifying
fabrication of the assembly.
* * * * *